Electrostatic printing head



March 18, 1969 A. MACOVSKI 3,434,157

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ALBERT 44A covs/o BY ,JM 4% A TTORNEY United States Patent Ofice 3,434,157 Patented Mar. 18, 1969 3,434,157 ELECTROSTATIC PRINTING HEAD Albert Macovski, Palo Alto, Calif., assignor to Stanford Research Institute, Menlo Park, Calif., a corporation of California Filed Feb. 4, 1966, Ser. No. 525,191 US. Cl. 346-74 4 Claims Int. Cl. G01d 15/06 This invention relates to electrostatic printing systems, and more particularly to an improved electrostatic printing head.

There is presently available an electrostatic printing system of a type wherein the ends of a plurality of wires or pins, which are arranged in a rectangular matrix, are brought to a common plane. Spaced from this common plane is a conductive ground plane or backplate. Paper upon which electrostatic printing is desired is interposed between the conductive backplate and the plane of the wire endings. A voltage is applied to selected ones of the wires which form the pattern of a character desired to be printed. The voltage is applied between these 'wire ends and the backplate with a value which exceeds the threshold required for depositing a charge upon the paper. The charge image deposited on the paper is then developed by having a suitable pigment powder applied thereto which adheres only to the regions which have the charge.

Normally a plurality of these printing heads are employed. They are placed adjacent one another. They are usually individually fabricated and the back ends of the wires which extend from each head are connected in parallel so that when the application of a voltage to one of these wires results in the voltage being applied to a' corresponding wire in each head. The backplate is provided for each head and by selective energization of the backplates, a determination is made at which of the parallel and side by side heads printing is to be permitted. The fabrication of the heads as well as their interconnections is complex, time consuming, and expensive. For example, an m n dot matrix with p character positions (a head for each character position) would take a total of mnp connections of the wire ends or pins. Thus a 5 x 7 matrix with a 100 character width printing head would have 3500 connections.

It is an object of this invention to provide a method and mean's of fabricating a dot matrix electrostatic printing head which is simpler than those employed heretofore.

Another object of this invention is the provision of a novel method and means for constructing a dot matrix electrostatic printing arrangement which requires considerably fewer interconnections.

Still another object of the present invention is the provision of a novel and unique electrostatic printing head arrangement.

These and other objects of the invention are achieved by using a thin flat strip, such as a shim, over which a multifilar helix is wound with m wires and p turns per wire. This provides a linear array of writing points with every mth point being interconnected. A total of n such shims are placed closely adjacent one another and then may be bonded together to form the matrix. Only n m total connections are brought out, since the multifilar helix automatically repeats the matrix p times. Thus, the construction and connection problems are drastically reduced.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as well as additional objects and advantages thereof, will 'best be undernection with the accompanying drawings, in which:

FIGURE 1 is a side, partial view of an embodiment of the invention;

FIGURE 2 is a bottom view of an embodiment of the invention; and

FIGURE 3 is a schematic diagram showing how the embodiment of the invention may be operated.

Referring now to FIGURE 1, there may be seen a perspective view of an embodiment of this invention. This comprises a number n of thin elongated members called shims, three of these respectively 10, 12, 14 being shown by way of example. Around each shim there is wound a multifilar helix containing m wires and there are p turns per helix. Thus, around the shim 10 there is wound, by way of example, four wires respectively 20, 22, 24, 26, of a multifilar helix, and there are p turns per wire. The number of shims times the number of wires in a helix determine the number of spots in a matrix. The number of helix turns determines how many times the matrix is duplicated. Since there are p turns per wire, the matrix is duplicated p times.

The second shim 12 also has a four wire multifilar helix, the wires respectively being designated as 20, 22', 24', 26'. The third shim 14 also has a four-wire multifilar helix thereon with each wire being respectively designated as 20", 22", 24", 26". The number of turns and the spacing of these turns on all of the shims is made the same. The shims are then abutted against one another in the manner shown in FIGURE 1. If the wires are not individually insulated, then it is necessary to either coat them with insulation before abutting or to use insulating spacers between adjacent shims. If the wires are insulated, then the shims may be abutted against one another. After the assembly of the n shims is completed, the entire assembly may have the insulation on the bottoms of the wires ground off. The assembly of shims may be held together by any suitable means such as by clamps or by suitable potting (not shown).

The appearance of the bottom end of the shims with the multifilar helices wound thereon may be seen in FIG- URE 2. It will be appreciated that the end of each wire turn corresponds to a pin or wire end in an electrostatic printing head of the type presently employed. The shims are narrow enough so that the bend of the wire effectively comprises a point. It should also be appreciated that with the technique described, one has constructed a dot printing electrostatic printing head for printing a line of characters consisting of p characters to a line and there is available for forming each character, n m dots. Further, all of the wires are automatically connected in parallel by the technique of fabrication.

Thus, as shown in FIGURE 1, the apparatus which performs the selective wire energization 30, need only be connected to and perform the selection of those of the n m wires which when energized describe the character desired to be printed. Either end of the multifilar helices is connected to the selective wire energization circuit 30'.

Spaced opposite each dot matrix formed by the ends of the wires there is placed a conductive ground plate respectively 40, 42, 44, 46 and 48. Since there are p dot matrices, there will be p of these conductive backplates. Between the backplates and the printing matrices paper 50, shown fragmentarily, is placed and is preferably in contact with both the matrices and the backplate. In order to effectuate electrostatic printing, the selected wire energization circuitry energizes those of the wires which form a dot pattern structure of the character desired to be printed, and a selective plate energization circuit 52 applies a potential to the one or more of the plates 40 through 48, which specify the location at which it is desired to form a charge image on the paper. After a line of image pattern charges have been deposited on the paper, the paper is moved to place a fresh strip in the printing position, while the strip upon which printing has occurred can then be developed using well-known xerographic techniques.

If it is desired to eifectuate continuous printing, then an arrangement of the type shown schematically in FIG- URE 3 may be employed. Here, a source of character signals 54 applies the signals to a converter 56 which performs the function of converting the character signals to wire selections. This is precisely the function performed with presently known dot matrix electrostatic printing heads. The output of the converter of character signals to wire selections will then comprise energization of those Wires which form a dot pattern of the character. Simultaneously with the application of character signals from the source 54 to the converter 56, a counter 58 is energized to cause its count to advance. The counter 58 is a cyclic counter and has its outputs respectively connected to the plates 40 through 48. Accordingly, the counter seeks to successively energize or select the plates with the successive characters from the signal source, thereby, each character is printed in its proper position in a line of characters. When the last plate 48 has been energized by the output of the counter 58, paper advance apparatus 60 is energized whereby the paper is advanced to present a fresh surface to the printing head. The counter, being a cyclic counter, upon the application of the next set of character signals, energizes the first of the plates 40.

It will be appreciated from the foregoing description that there has been described and shown a novel method and apparatus for making an electrostatic printing head of the dot matrix type. The technique is simple and can be used for making a head having any number of dot printing matrices without increasing the number of wire connections required to be made.

What is claimed is:

1. An improved electrostatic printing head of the dot matrix type comprising a plurality of thin elongated substantially rectangul-arly shaped members, on each member there being wound a multifilar wire helix, there being m wiresin each helix, and there being p winding turns of each helix around each member, the placement of the wire and the spacing of turns of each helix around each elongated member being substantially identical, said elongated members being placed adiacent one another with their fiat faces substantially parallel, to establish p dot matrices with the portions of the windings of said wire helices which pass around one of the edges of all of said elongated members.

2. The improvement recited in claim 1 wherein there is included means for selectively energizing those of the wire which form a dot pattern of a character desired to be printed, a conductive plate positioned opposite each of the dot matrices formed by the portions of the turns of said wire helices which extend around one of the edges of said plurality of elongated substantially rectangular members, and means for energizing the one of said conductive plates which define the position at which it is desired to print the character formed by the energized wires.

3. Apparatus as recited in claim 1 wherein said Wires are insulated and there are insulating spacers placed between adjacent elongated substantially rectangular members.

4. An electrostatic dot matrix printing head comprising a plurality of thin shims placed adjacent one another, each shim having wound thereon a multifilar wire helix, the number of wires in each helix and the number of turns of each helix on each shim being identical, the wires and the turns of the wires of the helix on each shim being disposed in substantial alignment to form at one of the edges of said shims a wire dot electrostatic printing matrix, means for applying energizing potential to those of the wires of all of 'said multifilar windings which provide a dot image pattern of a character desired to be printed, and plate means spaced opposite each one of the dot printing matrices established for determining at which one of these matrices printing of said character should occur.

References Cited UNITED STATES PATENTS 2,930,847 3/1960 .Metzger 346-74 3,034,124 5/1962 Anderson 346-74 3,267,485 8/1966 Howell 34674 TERRELL W. FEARS, Primary Examiner. LEE J. SCH ROEDER, Assistant Examiner.

US. Cl. X.'R. 346139 

1. AN IMPROVED ELECTROSTATIC PRINTING HEAD OF THE DOT MATRIX TYPE COMPRISING A PLURALITY OF THIN ELONGATED SUBSTANTIALLY RECTANGULARLY SHAPED MEMBERS, ON EACH MEMBER THERE BEING WOUND A MULTIFILAR WIRE HELIX, THERE BEING M WIRES IN EACH HELIX, AND THERE BEING P WINDING TURNS OF EACH HELIX AROUND EACH MEMBER, THE PLACEMENT OF THE WIRE AND THE SPACING OF TURNS OF EACH HELIX AROUND EACH ELONGATED MEMBER BEING SUBSTANTIALLY IDENTICAL, SAID ELONGATED MEMBERS BEING PLACED ADJACENT ONE ANOTHER WITH THEIR FLAT FACES SUBSTANTIALLY PARALLEL, TO ESTABLISH P DOT MATRICES WITH THE PORTIONS OF THE WINDINGS OF SAID WIRE HELICES WHICH PASS AROUND ONE OF THE EDGES OF ALL OF SAID ELONGATED MEMBERS. 